Titin and ryanodine receptor epitopes are expressed in cortical thymoma along with costimulatory molecules

Case Report: Telitacicept in severe myasthenia gravis: a case study with multiple autoantibodies

Multi-antibody-positive myasthenia gravis (MG) presentations are relatively rare, often found in older patients, and generally predict a poor prognosis. We report a case of a female patient with generalized MG, testing positive for Titin antibodies (Titin-Ab), ryanodine receptor antibodies (RyR-Ab), and acetylcholine receptor antibodies (AChR-Ab), and resistant to acetylcholinesterase inhibitors. Following unsuccessful traditional therapies, she received Telitacicept, leading to significant improvements. This case underscores Telitacicept's potential efficacy for similar patients and offers insights into the clinical characteristics of multi-antibody MG.

Immunologic Significance of CD80/CD86 or Major Histocompatibility Complex-II Expression in Thymic Epithelial Tumors

Introduction

Unresectable or recurrent thymic epithelial tumors (TETs) have a poor prognosis, and treatment options are limited. This study aimed to investigate the immunologic significance of CD80/CD86 or major histocompatibility complex class II (MHC-II) expression in TETs, as potential predictive biomarkers for immune checkpoint inhibitors (ICIs).

Methods

We analyzed CD80, CD86, MHC class I (MHC-I), and MHC-II expression in TETs using immunohistochemistry and investigated their association with T-cell infiltration or ICI efficacy. In addition, we generated CD80- or MHC-II-expressing mouse tumors, evaluated the effects of ICIs, and analyzed tumor-infiltrating lymphocytes. We also performed tumor-rechallenge experiments in vivo.

Results

We found that approximately 50% and 30% of TETs had high expression of CD80/CD86 and MHC-II in tumor cells, respectively, and that this expression was related to T-cell infiltration in clinical samples. In mouse models, both CD80 and MHC-II increase the effects of ICIs. In addition, senescent T cells and long-lived memory precursor effector T cells were significantly decreased and increased, respectively, in tumor-infiltrating lymphocytes from CD80-expressing tumors, and rechallenged tumors were completely rejected after the initial eradication of CD80-expressing tumors by programmed cell death protein 1 blockade. Indeed, patients with CD80-high thymic carcinoma had longer progression-free survival with anti-programmed cell death protein 1 monoclonal antibody.

Conclusions

Half of the TETs had high expression of CD80/CD86 or MHC-II with high T-cell infiltration. These molecules could potentially increase the effects of ICIs, particularly inducing a durable response. CD80/CD86 and MHC-II can be predictive biomarkers of ICIs in TETs, promoting the development of drugs for such TETs.

Functional autoantibodies: Definition, mechanisms, origin and contributions to autoimmune and non-autoimmune disorders

A growing body of evidence underscores the relevance of functional autoantibodies in the development of various pathogenic conditions but also in the regulation of homeostasis. However, the definition of functional autoantibodies varies among studies and a comprehensive overview on this emerging topic is missing. Here, we do not only explain functional autoantibodies but also summarize the mechanisms underlying the effect of such autoantibodies including receptor activation or blockade, induction of receptor internalization, neutralization of ligands or other soluble extracellular antigens, and disruption of protein-protein interactions. In addition, in this review article we discuss potential triggers of production of functional autoantibodies, including infections, immune deficiency and tumor development. Finally, we describe the contribution of functional autoantibodies to autoimmune diseases including autoimmune thyroid diseases, myasthenia gravis, autoimmune pulmonary alveolar proteinosis, autoimmune autonomic ganglionopathy, pure red cell aplasia, autoimmune encephalitis, pemphigus, acquired thrombotic thrombocytopenic purpura, idiopathic dilated cardiomyopathy and systemic sclerosis, as well as non-autoimmune disorders such as allograft rejection, infectious diseases and asthma.

Atypical Seropositive Striated Muscle Antibody Myasthenia Gravis Presentation With Metastatic B1 Thymoma: A Rare Case

The association between myasthenia gravis (MG) and thymomas is well-documented. Thymomas are rare epithelial cell tumors that arise from the thymus gland and occur in the mediastinum. Myasthenia gravis is a neuromuscular disorder that causes skeletal muscle weakness due to the presence of anti-acetylcholinesterase antibodies. Roughly 60% of thymomas are associated with MG, while only 10% of MG patients have thymomas. We present an atypical presentation of myasthenia gravis with an associated unusual metastatic thymoma. This case is of a young, previously healthy 26-year-old male with no previous medical history who presented with non-specific symptoms of fatigue, diarrhea, abdominal pain, back pain, blurry vision, and unintended weight loss. He underwent treatment with intravenous immunoglobulins (IVIG), had two surgical resections of the thymoma, and ultimately received radiotherapy. Based on our experience with this case, diagnosing myasthenia gravis by testing for specific muscle antibodies for patients with ptosis in the setting of non-specific complaints, including fatigue, vomiting, diarrhea, and abdominal or back pain, should be considered. Routine imaging should follow with a chest computed tomography to screen for thymomas if the specific anti-titin and anti-ryanodine receptor (anti-RyR) muscle antibodies are positive and myasthenia gravis is suspected. If a thymoma is confirmed, it is best to confirm; and mass characterizes with chest magnetic resonance imaging. A treatment approach of IVIG followed by surgical resection and possible debulking if the lesion is deemed metastatic could also be considered thereafter, especially in young patients with few comorbidities. Treatment with Pyridostigmine 30 mg twice daily for 25 days post-surgically and radiation for treatment of any remaining unresectable tumor should also be considered.

Exploring the Gut Microbiome in Myasthenia Gravis

The human gut microbiota is vital for maintaining human health in terms of immune system homeostasis. Perturbations in the composition and function of microbiota have been associated with several autoimmune disorders, including myasthenia gravis (MG), a neuromuscular condition associated with varying weakness and rapid fatigue of the skeletal muscles triggered by the host’s antibodies against the acetylcholine receptor (AChR) in the postsynaptic muscle membrane at the neuromuscular junction (NMJ). It is hypothesized that perturbation of the gut microbiota is associated with the pathogenesis of MG. The gut microbiota community profiles are usually generated using 16S rRNA gene sequencing. Compared to healthy individuals, MG participants had an altered gut microbiota’s relative abundance of bacterial taxa, particularly with a drop in Clostridium. The microbial diversity related to MG severity and the overall fecal short-chain fatty acids (SCFAs) were lower in MG subjects. Changes were also found in terms of serum biomarkers and fecal metabolites. A link was found between the bacterial Operational Taxonomic Unit (OTU), some metabolite biomarkers, and MG’s clinical symptoms. There were also variations in microbial and metabolic markers, which, in combination, could be used as an MG diagnostic tool, and interventions via fecal microbiota transplant (FMT) could affect MG development. Probiotics may influence MG by restoring the gut microbiome imbalance, aiding the prevention of MG, and lowering the risk of gut inflammation by normalizing serum biomarkers. Hence, this review will discuss how alterations of gut microbiome composition and function relate to MG and the benefits of gut modulation.

Characteristics, treatment, and outcomes of Myasthenia Gravis in COVID-19 patients: A systematic review

Objective

Recent studies suggest that the clinical course and outcomes of patients with coronavirus disease 2019 (COVID-19) and myasthenia gravis (MG) are highly variable. We performed a systematic review of the relevant literature with a key aim to assess the outcomes of invasive ventilation, mortality, and hospital length of stay (HLoS) for patients presenting with MG and COVID-19.

Methods

We searched the PubMed, Scopus, Web of Science, and MedRxiv databases for original articles that reported patients with MG and COVID-19. We included all clinical studies that reported MG in patients with confirmed COVID-19 cases via RT-PCR tests. We collected data on patient background characteristics, symptoms, time between MG and COVID-19 diagnosis, MG and COVID-19 treatments, HLoS, and mortality at last available follow-up. We reported summary statistics as counts and percentages or mean±SD. When necessary, inverse variance weighting was used to aggregate patient-level data and summary statistics.

Results

Nineteen studies with 152 patients (mean age 54.4 ± 12.7 years; 79/152 [52.0%] female) were included. Hypertension (62/141, 44.0%) and diabetes (30/141, 21.3%) were the most common comorbidities. The mean time between the diagnosis of MG and COVID-19 was7.0 ± 6.3 years. Diagnosis of COVID-19 was confirmed in all patients via RT-PCR tests. Fever (40/59, 67.8%) and ptosis (9/55, 16.4%) were the most frequent COVID-19 and MG symptoms, respectively. Azithromycin and ceftriaxone were the most common COVID-19 treatments, while prednisone and intravenous immunoglobulin were the most common MG treatments. Invasive ventilation treatment was required for 25/59 (42.4%) of patients. The mean HLoS was 18.2 ± 9.9 days. The mortality rate was 18/152 (11.8%).

Conclusion

This report provides an overview of the characteristics, treatment, and outcomes of MG in COVID-19 patients. Although COVID-19 may exaggerate the neurological symptoms and worsens the outcome in MG patients, we did not find enough evidence to support this notion. Further studies with larger numbers of patients with MG and COVID-19 are needed to better assess the clinical outcomes in these patients.

Heterogeneity in myasthenia gravis: considerations for disease management

Introduction: Myasthenia gravis is a rare disease of the neuromuscular junction and a prototype of B cell-driven immunopathology. Pathogenic antibodies target post-synaptic transmembrane proteins, most commonly the nicotinic acetylcholine receptor and the muscle-specific tyrosine kinase, inducing end-plate alterations and neuromuscular transmission impairment. Several clinical subtypes are distinct on the basis of associated antibodies, age at symptom onset, thymus pathology, genetic factors, and weakness distribution. These subtypes have distinct pathogenesis that can account for different responses to treatment. Conventional therapy is based on the use of symptomatic agents, steroids, immunosuppressants and thymectomy. Of late, biologics have emerged as effective therapeutic options.Areas covered: In this review, we will discuss the management of myasthenia gravis in relation to its phenotypic and biological heterogeneity, in the light of recent advances in the disease immunopathology, new diagnostic tools, and results of clinical trialsExpert opinion: Clinical management is shaped on serological subtype, and patient age at onset, lifestyle and comorbidities, balancing therapeutic needs and safety. Although reliable biomarkers predictive of clinical and biologic outcome are still lacking, recent developments promise a more effective and safe treatment. Disease subtyping according to serological testing and immunopathology is crucial to the appropriateness of clinical management.

Fc-Receptor Targeted Therapies for the Treatment of Myasthenia gravis

Myasthenia gravis (MG) is an autoimmune disease in which immunoglobulin G (IgG) antibodies (Abs) bind to acetylcholine receptors (AChR) or to functionally related molecules in the postsynaptic membrane at the neuromuscular junction. IgG crystallizable fragment (Fc)-mediated effector functions, such as antibody-dependent complement deposition, contribute to disease development and progression. Despite progress in understanding Ab-mediated disease mechanisms, immunotherapy of MG remained rather unspecific with corticosteroids and maintenance with immunosuppressants as first choice drugs for most patients. More specific therapeutic IgG Fc-based platforms that reduce serum half-life or effector functions of pathogenic MG-related Abs are currently being developed, tested in clinical trials or have recently been successfully translated into the clinic. In this review, we illustrate mechanisms of action and clinical efficacies of emerging Fc-mediated therapeutics such as neonatal Fc receptor (FcRn)-targeting agents. Furthermore, we evaluate prospects of therapies targeting classical Fc receptors that have shown promising therapeutic efficacy in other antibody-mediated conditions. Increased availability of Fc- and Fc receptor-targeting biologics might foster the development of personalized immunotherapies with the potential to induce sustained disease remission in patients with MG.

Thymus and autoimmunity

The thymus prevents autoimmune diseases through mechanisms that operate in the cortex and medulla, comprising positive and negative selection and the generation of regulatory T-cells (Tregs). Egress from the thymus through the perivascular space (PVS) to the blood is another possible checkpoint, as shown by some autoimmune/immunodeficiency syndromes. In polygenic autoimmune diseases, subtle thymic dysfunctions may compound genetic, hormonal and environmental cues. Here, we cover (a) tolerance-inducing cell types, whether thymic epithelial or tuft cells, or dendritic, B- or thymic myoid cells; (b) tolerance-inducing mechanisms and their failure in relation to thymic anatomic compartments, and with special emphasis on human monogenic and polygenic autoimmune diseases and the related thymic pathologies, if known; (c) polymorphisms and mutations of tolerance-related genes with an impact on positive selection (e.g. the gene encoding the thymoproteasome-specific subunit, PSMB11), promiscuous gene expression (e.g. AIRE, PRKDC, FEZF2, CHD4), Treg development (e.g. SATB1, FOXP3), T-cell migration (e.g. TAGAP) and egress from the thymus (e.g. MTS1, CORO1A); (d) myasthenia gravis as the prototypic outcome of an inflamed or disordered neoplastic ‘sick thymus’.

Neonatal thymectomy in children-accelerating the immunologic clock?

The thymus is critical for central tolerance and diverse T-lymphocyte repertoire development, to provide lifelong defense against pathogens while maintaining self-tolerance. Peak thymic output occurs in utero, during infancy, and in early childhood, diminishing throughout life. Infants with congenital heart disease requiring sternotomy often undergo thymectomy to clear the surgical field. The long-term effects of early thymectomy are just being appreciated. Many patients remain asymptomatic despite immunologic findings mirroring those of immunosenescence. Few develop increased infection or lymphoreticular malignancy risk. When considering the effects of infant thymectomy, patients with partial DiGeorge syndrome or hypomorphic recombination-activating gene (RAG) mutations may be instructive. These patients are lymphocytopenic, with increased early-onset infection and autoimmunity risk that is not seen in most patients who underwent thymectomy during infancy. The thymic structure of patients with partial DiGeorge syndrome or hypomorphic RAG is abnormal, with disrupted architecture inclining to perturbation of central tolerance. Similar findings may be seen in patients with myasthenia gravis, although disrupted peripheral tolerance may play a greater role in autoimmunity development. In conclusion, thymectomy during infancy may increase future risk of infection or autoimmunity, with premature immunosenescence mediated through disruption of central and peripheral tolerance mechanisms initiated by early cessation or diminution of thymic output. Ideally, some thymic tissue should be preserved at the time of surgery.

Thymoma associated myasthenia gravis with atypical presentation of lipomatous tongue atrophy: a case report

A 28-year-old female patient came to the outpatient dental clinic for multiple teeth extractions and full mouth rehabilitation suffer from myasthenia gravis (MG) primary presentation as tongue atrophy and facial muscles weakness and the symptoms became worries, the patient unable to speak as well and change her voice and complaining of dysphagia and dysarthria. Oral symptoms, treatment schedule and protocol, the selection, prescription and impacts of medications, and prevention of myasthenic crisis are all important; aspects should be considered by dentists and oral health care providers. Weakness of facial and oropharyngeal muscle is considered very popular at disease onset and therefore oral health providers are often the first medical professionals to observe these patients. Myasthenic patients seek particular approach and consultation in order to ensure ideal and proper dental management.

Increased costimulatory molecule expression of thymic and peripheral B cells and a sensitivity to IL-21 in myasthenia gravis

B cells may contribute to the pathogenesis of myasthenia gravis with anti-acetylcholine antibodies (AChR+ MG) by co-stimulation or selection of T cells. In this study, we investigated costimulatory molecules on B cells in the blood and in the thymus as well as by TLR9 and IL-21 stimulations in AChR+ MG patients with or without immunosuppressive treatment and controls. CD80 and CD86 expression on B cells was increased in the peripheral blood and in the thymus of untreated patients. CD86 was further amplified by IL-21. A role for activated B cells, active thymic environment and IL-21 is implicated in MG.

The Integrated Genomic Landscape of Thymic Epithelial Tumors

Thymic epithelial tumors (TETs) are one of the rarest adult malignancies. Among TETs, thymoma is the most predominant, characterized by a unique association with autoimmune diseases, followed by thymic carcinoma, which is less common but more clinically aggressive. Using multi-platform omics analyses on 117 TETs, we define four subtypes of these tumors defined by genomic hallmarks and an association with survival and World Health Organization histological subtype. We further demonstrate a marked prevalence of a thymoma-specific mutated oncogene, GTF2I, and explore its biological effects on multi-platform analysis. We further observe enrichment of mutations in HRAS, NRAS, and TP53. Last, we identify a molecular link between thymoma and the autoimmune disease myasthenia gravis, characterized by tumoral overexpression of muscle autoantigens, and increased aneuploidy.

Low conversion rate of ocular to generalized myasthenia gravis in Singapore

INTRODUCTION

Ocular myasthenia gravis (OMG) is a common condition of the neuromuscular junction that may convert to generalized myasthenia gravis (GMG). Our aim in this study was to determine the conversion rate and predictive factors for generalization in OMG, in an Asian population.

METHODS

The investigation consisted of a retrospective study of OMG patients with a minimum 2 years of follow-up.

RESULTS

Among 191 patients with OMG, 155 had the minimum 2-year follow-up. The conversion rate at median follow-up (40.8 months) was 10.6% (95% confidence interval 7.9%-13.3%), and at the 2-year follow-up it was 7.7% (95% confidence interval 5.6%-9.8%). At baseline, the predictive factors for generalization were positive acetylcholine receptor antibodies (hazard ratio 3.71, P = 0.024), positive repetitive nerve stimulation (RNS) studies (hazard ratio 4.42, P = 0.003), and presence of radiologically presumed or pathologically confirmed thymoma (hazard ratio 3.10, P = 0.013).

DISCUSSION

The conversion rate of OMG to GMG in Asian patients is low, as predicted by presence of acetylcholine receptor antibodies, presence of thymoma, and positive RNS studies. Muscle Nerve 57: 756-760, 2018.

Clinical features, pathogenesis, and treatment of myasthenia gravis: a supplement to the Guidelines of the German Neurological Society

Myasthenia gravis (MG) is an autoimmune antibody-mediated disorder of neuromuscular synaptic transmission. The clinical hallmark of MG consists of fluctuating fatigability and weakness affecting ocular, bulbar and (proximal) limb skeletal muscle groups. MG may either occur as an autoimmune disease with distinct immunogenetic characteristics or as a paraneoplastic syndrome associated with tumors of the thymus. Impairment of central thymic and peripheral self-tolerance mechanisms in both cases is thought to favor an autoimmune CD4(+) T cell-mediated B cell activation and synthesis of pathogenic high-affinity autoantibodies of either the IgG1 and 3 or IgG4 subclass. These autoantibodies bind to the nicotinic acetylcholine receptor (AchR) itself, or muscle-specific tyrosine-kinase (MuSK), lipoprotein receptor-related protein 4 (LRP4) and agrin involved in clustering of AchRs within the postsynaptic membrane and structural maintenance of the neuromuscular synapse. This results in disturbance of neuromuscular transmission and thus clinical manifestation of the disease. Emphasizing evidence from clinical trials, we provide an updated overview on immunopathogenesis, and derived current and future treatment strategies for MG divided into: (a) symptomatic treatments facilitating neuromuscular transmission, (b) antibody-depleting treatments, and

Myf5 and Myogenin in the development of thymic myoid cells - Implications for a murine in vivo model of myasthenia gravis

Myasthenia gravis (MG) is caused by autoantibodies against the neuromuscular junction of striated muscle. Most MG patients have autoreactive T- and B-cells directed to the acetylcholine receptor (AChR). To achieve immunologic tolerance, developing thymocytes are normally eliminated after recognition of self-antigen-derived peptides. Presentation of muscle-specific antigens is likely achieved through two pathways: on medullary thymic epithelial cells and on medullary dendritic cells cross-presenting peptides derived from a unique population of thymic myoid cells (TMC). Decades ago, it has been hypothesized that TMC play a key role in the induction of immunological tolerance towards skeletal muscle antigens. However, an experimental model to address this postulate has not been available. To generate such a model, we tested the hypothesis that the development of TMC depends on myogenic regulatory factors. To this end, we utilized Myf5-deficient mice, which lack the first wave of muscle cells but form normal skeletal muscles later during development, and Myogenin-deficient mice, which fail to form differentiated myofibers. We demonstrate for the first time that Myf5- and Myogenin-deficient mice showed a partial or complete, respectively, loss of TMC in an otherwise regularly structured thymus. To overcome early postnatal lethality of muscle-deficient, Myogenin-knockout mice we transplanted Myogenin-deficient fetal thymuses into Foxn1(nu/nu) mice that lack their own thymus anlage. We found that the transplants are functional but lack TMC. In combination with established immunization strategies (utilizing AChR or Titin), this model should enable us in the future testing the hypothesis that TMC play an indispensable role in the development of central tolerance towards striated muscle antigens.

Thymoma related myasthenia gravis in humans and potential animal models

Thymoma-associated Myasthenia gravis (TAMG) is one of the anti-acetylcholine receptor MG (AChR-MG) subtypes. The clinico-pathological features of TAMG and its pathogenesis are described here in comparison with pathogenetic models suggested for the more common non-thymoma AChR-MG subtypes, early onset MG and late onset MG. Emphasis is put on the role of abnormal intratumorous T cell selection and activation, lack of intratumorous myoid cells and regulatory T cells as well as deficient expression of the autoimmune regulator (AIRE) by neoplastic thymic epithelial cells. We review spontaneous and genetically engineered thymoma models in a spectrum of animals and the extensive clinical and immunological overlap between canine, feline and human TAMG. Finally, limitations and perspectives of the transplantation of human and murine thymoma tissue into nude mice, as potential models for TAMG, are addressed.

Expression and polymorphisms of T cell immunoglobulin domain and mucin domain protein-1 in thymoma with or without myasthenia gravis

The present study aimed to investigate the expression and association of the single-nucleotide polymorphism (SNP) -1637A/G in the promoter region of the T cell immunoglobulin domain and mucin domain protein-1 (Tim-1) gene in patients diagnosed with thymoma with or without myasthenia gravis (MG). The expression of Tim-1 was detected using the streptavidin peroxidase immunohistochemical staining method on tissues obtained from thymoma patients with (n=58) and without (n=62) MG. The Tim-1 gene -1637A/G polymorphism was detected using the single allele-specific primer polymerase chain reaction. The positive rate of Tim-1 expression in thymoma patients with MG was 62.1% (32/58), which was significantly higher compared with that in thymoma patients without MG (33.9%, 21/62) (P=0.002). The genotype frequencies of GG, GA and AA in the -1637A/G polymorphism were 0.7931, 0.2069 and 0, respectively, in thymoma patients with MG, and 0.6129, 0.3871 and 0, respectively, in thymoma patients without MG. A significant difference in the genotypes between the thymoma patients with MG and those without MG was found (P=0.031). In addition, a significant difference in allele frequencies between thymoma patients with MG and those without MG (P=0.024) was observed. The high expression of Tim-1 in thymoma tissues may play an important role in the development of thymoma with MG. The -1637A/G polymorphism site of the promoter region in Tim-1 may be associated with thymoma with MG. These findings provide a basis for further genetic research of thymoma with MG.

[Thymoma-associated myasthenia gravis: Clinical features and surgical results]

OBJECTIVE

The aim of this study was to compare the characteristics of myasthenic patients with and without thymoma, and the results of thymectomy in both types of patients.

MATERIAL AND METHODS

A retrospective study was conducted among 66 patients who underwent thymectomy for myasthenia gravis in our department over a 10-year period (2000-2010). The surgical approach was sternotomy or anterolateral thoracotomy. Patients were divided into two groups according to the presence of thymoma: with (T-MG) and without (NT-MG) thymoma. Complete stable remission (CSR) was the primary endpoint.

RESULTS

Median age was 35.09±9.89 years. The NT-MG group had 38 patients (57.57%) and the T-MG group 28 patients (42.43%). There was no difference between the two groups regarding the surgical approach (P=0.52). T-MG patients were older (40.54±15.16 vs. 31.37±9.46) (P=0.008) and predominantly male. There were more generalized forms (P=0.01) and more bulbar involvement (P=0.02) in the T-MG group. The rate of CSR at 5 years was 7% and 17% in the T-MG and NT-MG patients respectively (P=0.70). At 10 years, it was 36% and 94.73% respectively (P=0.03).

CONCLUSION

Thymomatous myasthenia gravis is characterized by the severity of its clinical features. Remission rate at 10 years was significantly lower in the myasthenia with thymoma group.

Muscle autoantibodies in myasthenia gravis: beyond diagnosis?

Myasthenia gravis is an autoimmune disorder of the neuromuscular junction. A number of molecules, including ion channels and other proteins at the neuromuscular junction, may be targeted by autoantibodies leading to abnormal neuromuscular transmission. In approximately 85% of patients, autoantibodies, directed against the postsynaptic nicotinic acetylcholine receptor can be detected in the serum and confirm the diagnosis, but in general, do not precisely predict the degree of weakness or response to therapy. Antibodies to the muscle-specific tyrosine kinase are detected in approximately 50% of generalized myasthenia gravis patients who are seronegative for anti-acetylcholine receptor antibodies, and levels of anti-muscle-specific tyrosine kinase antibodies do appear to correlate with disease severity and treatment response. Antibodies to other muscle antigens may be found in the subsets of myasthenia gravis patients, potentially providing clinically useful diagnostic information, but their utility as relevant biomarkers (measures of disease state or response to treatment) is currently unclear.

Thymoma in myasthenia gravis: from diagnosis to treatment

One half of cortical thymoma patients develop myasthenia gravis (MG), while 15% of MG patients have thymomas. MG is a neuromuscular junction disease caused in 85% of the cases by acetylcholine receptor (AChR) antibodies. Titin and ryanodine receptor (RyR) antibodies are found in 95% of thymoma MG and 50% of late-onset MG (MG onset ≥50 years), are associated with severe disease, and may predict thymoma MG outcome. Nonlimb symptom profile at MG onset with bulbar, ocular, neck, and respiratory symptoms should raise the suspicion about the presence of thymoma in MG. The presence of titin and RyR antibodies in an MG patient younger than 60 years strongly suggests a thymoma, while their absence at any age strongly excludes thymoma. Thymoma should be removed surgically. Prethymectomy plasmapheresis/iv-IgG should be considered before thymectomy. The pharmacological treatment does not differ from nonthymoma MG, except for tacrolimus which is an option in difficult thymoma and nonthymoma MG cases with RyR antibodies.

Three types of striational antibodies in myasthenia gravis

Myasthenia gravis (MG) is caused by antibodies that react mainly with the acetylcholine receptor on the postsynaptic site of the neuromuscular junction. A wide range of clinical presentations and associated features allow MG to be classified into subtypes based on autoantibody status. Striational antibodies, which react with epitopes on the muscle proteins titin, ryanodine receptor (RyR), and Kv1.4, are frequently found in MG patients with late-onset and thymoma. Antititin and anti-RyR antibodies are determined by enzyme-linked immunosorbent assay or immunoblot. More recently, a method for the detection of anti-Kv1.4 autoantibodies has become available, involving 12-15% of all MG patients. The presence of striational antibodies is associated with more severe disease in all MG subgroups. Anti-Kv1.4 antibody is a useful marker for the potential development of lethal autoimmune myocarditis and response to calcineurin inhibitors. Detection of striational antibodies provides more specific and useful clinical information in MG patients.

Management of myasthenic patients with thymoma

Myasthenia gravis (MG) associated with thymomas differs from nonthymomatous MG, and thymomas associated with MG are also different from non-MG thymomas. According to the World Health Organization classification, the incidence of MG in thymomas was the highest in the subtypes B2, B1, and AB. Transsternal approach is still regarded as the gold standard for surgical treatment of thymomas. Less-invasive techniques of thymectomy are promising, but it is too early to estimate their real oncological value. In the series including more than 100 patients, the prognosis for survival is better in patients with thymomas associated with MG than in those with non-MG thymomas, and the prognosis for patients with MG associated with thymoma is worse than that for patients with nonthymomatous MG.

The auto-antigen repertoire in myasthenia gravis

Myasthenia Gravis (MG) is an antibody-mediated autoimmune disorder affecting the postsynaptic membrane of the neuromuscular junction (NMJ). MG is characterized by an impaired signal transmission between the motor neuron and the skeletal muscle cell, caused by auto-antibodies directed against NMJ proteins. The auto-antibodies target the nicotinic acetylcholine receptor (nAChR) in about 90% of MG patients. In approximately 5% of MG patients, the muscle specific kinase (MuSK) is the auto-antigen. In the remaining 5% of MG patients, however, antibodies against the nAChR or MuSK are not detectable (idiopathic MG, iMG). Although only the anti-nAChR and anti-MuSK auto-antibodies have been demonstrated to be pathogenic, several other antibodies recognizing self-antigens can also be found in MG patients. Various auto-antibodies associated with thymic abnormalities have been reported, as well as many non-MG-specific auto-antibodies. However, their contribution to the cause, pathology and severity of the disease is still poorly understood. Here, we comprehensively review the reported auto-antibodies in MG patients and discuss their role in the pathology of this autoimmune disease.

The autoimmune regulator AIRE in thymoma biology: autoimmunity and beyond

Thymomas are tumors of thymic epithelial cells. They associate more often than any other human tumors with various autoimmune diseases; myasthenia gravis is the commonest, occurring in 10-50% of thymoma patients, depending on the World Health Organization-defined histologic subtype. Most thymomas generate many polyclonal maturing T lymphocytes but in disorganized microenvironments Failure to induce self-tolerance may be a key factor leading to the export of potentially autoreactive CD4 progeny, thus predisposing to autoimmune diseases. Normally, the master Autoimmune Regulator promotes expression of peripheral tissue-restricted antigens such as insulin by medullary thymic epithelial cells and induction of tolerance to them. The failure of approximately 95% of thymomas to express autoimmune regulator is another feature potentially contributing to autoimmunity.

Thymoma and paraneoplastic myasthenia gravis

Paraneoplastic autoimmune diseases associate occasionally with small cell lung cancers and gynecologic tumors. However, myasthenia gravis (MG) occurs in at least 30% of all patients with thymomas (usually present at MG diagnosis). These epithelial neoplasms almost always have numerous admixed maturing polyclonal T cells (thymocytes). This thymopoiesis-and export of mature CD4(+)T cells-particularly associates with MG, though there are rare/puzzling exceptions in apparently pure epithelial WHO type A thymomas. Other features potentially leading to inefficient self-tolerance induction include defective epithelial expression of the autoimmune regulator (AIRE) gene and/or of major histocompatibility complex class II molecules in thymomas, absence of myoid cells, failure to generate FOXP3(+) regulatory T cells, and genetic polymorphisms affecting T-cell signaling. However, the strong focus on MG/neuromuscular targets remains unexplained and suggests some biased autoantigen expression, T-cell selection, or autoimmunization within thymomas. There must be further clues in the intriguing serological and cellular parallels in some patients with late-onset MG but without thymomas-and in others with AIRE mutations-and in the contrasts with early-onset MG, as discussed here.

Thymomas: review of current clinical practice

Thymomas are the most common tumors of the mediastinum. The introduction of multimodality treatment strategies, as well as novel approaches to the diagnosis of these tumors, has led to changes in the clinical management of thymomas. Here we review the literature for current clinical practice in the diagnosis, management, and treatment of thymomas.

Autoimmunizing mechanisms in thymoma and thymus

Autoimmunizing mechanisms are very hard to study in humans, so we have focused on vital clues in thymomas and hyperplastic thymuses in myasthenia gravis (MG). According to our multi-step hypothesis: thymic epithelial cells (TEC) present epitopes from the isolated acetylcholine receptor (AChR) subunits they express, and autoimmunize helper T cells; subsequently, these evoke "early antibodies" that then attack rare thymic myoid cells expressing intact AChR; in the resulting germinal centers, autoantibodies diversify to recognize native AChR. We have studied: 1) thymomas, to identify autoimmunizing cell types, focusing on IFN-alpha, against which many patients have high titer autoantibodies, as in another highly informative autoimmune syndrome. Although IFN-alpha is much easier to label than the sparse and delicate AChR subunits, we have not yet located obviously autoimmunizing micro-environments; 2) hyperplastic MG thymuses, where we find (a) upregulation of complement receptors and regulators on hyperplastic TEC and deposition of activated C3b complement component on them, (b) absence of complement regulators from almost all myoid cells, indicating vulnerability to attack, and (c) deposition of C3b, and even of the terminal membrane attack complex, especially on the myoid cells close to the infiltrating germinal centers. The changes are very similar in over 50% of the so-called seronegative patients with generalized MG (SNMG) but without detectable autoantibodies against AChR or MuSK, consistently with other evidence that they belong to the spectrum of AChR-seropositive MG. Together, moreover, our findings implicate both myoid cells and TEC in autoimmunization, and thus strongly support our hypothesis.

Hypothetical review: thymic aberrations and type-I interferons; attempts to deduce autoimmunizing mechanisms from unexpected clues in monogenic and paraneoplastic syndromes

In sporadic autoimmune disorders, dendritic cells are increasingly being incriminated as agents provocateurs. However, the mechanisms and any 'danger signals' that induce them to autoimmunize remain enigmatic. Here, we focus on unexpected clues from two prototypic/ highly informative autoimmune syndromes, acquired thymoma-associated myasthenia gravis and the monogenic autoimmune polyendocrine syndrome type-1 (APS1), caused by mutations in the AutoImmune Regulator (AIRE). Both involve the thymus, and in both we find early, persistent, highly prevalent and high-titre neutralizing autoantibodies against type-I interferons, regardless of the exact AIRE genotype or the characteristically variable clinical phenotype in APS1. Thus these key innate<-->adaptive immune intermediaries are now implicated in APS1 and paraneoplastic myasthenia as well as in systemic lupus erythematosus and other sporadic autoimmune disorders. The currently accepted notion that autoimmunization proceeds automatically (by 'default') does not explain how, when or where autoimmune responses are initiated against which targets in APS1, or whether exogenous or internal danger signals are involved, or predict whether the primary auto-immunogenic targets are AIRE-dependent. As the parallels between these syndromes must hold novel clues to these puzzles, they demand explanations. To unify these and other findings, we propose that autoimmunization occurs centrally in aberrant thymic environments rendered 'dangerous' by AIRE-deficiency (possibly by excess undegraded nucleic acids/dead cell debris). The ensuing autoreactivity focuses early on the locally abundant type I interferons and then on other peripheral tissue autoantigens that are still expressed despite the absence of AIRE. These ideas raise numerous questions that others may already have the materials to address.

Autoantibodies against TRPC3 and ryanodine receptor in myasthenia gravis

The transient receptor potential canonical type-3 (TRPC3, receptor- and store-operated Ca(2+) influx channel) participates in skeletal muscle contraction; its functional interactions with ryanodine receptor-1 (RyR1) are independent of sarcoplasmic Ca(2+) content and dihydropyridine receptor. In 25 generalized myasthenia gravis (MG), we detected antibodies against human TRPC3 peptide in 9 patients (8 with thymoma and one with hyperplastic thymus) and those against human RyR1 peptides in 16 patients (15 with thymoma and one with hyperplastic thymus). Both antibodies were found in patients with more severe myasthenia and could contribute to the contractile abnormalities in MG.

Titin and ryanodine receptor antibodies and neuromuscular involvement in myasthenia gravis

Of sera of patients with myasthenia gravis (MG), 30% contains titin and ryanodine receptor (RyR) antibodies. In early-onset MG (i.e., before 50 years of age), the presence of titin antibodies strongly suggests a thymoma. Late-onset MG comprises one MG group, characterized by a broad antimuscle immune response, including both titin and the acetylcholine receptor (AChR). Another group is preferentially associated with the HLA-A3, B7 and DRw2 antigens, representing a delayed early-onset of the disease that has a selective AChR immune response. The presence of titin and RyR antibodies is associated with more severe disease. Titin antibodies may, in some patients with rippling muscle disease, affect the contractile machinery of myofibers, thereby affecting their mechanical sensitivity. It is not known whether this occurs in MG. RyR antibodies may impair excitation–contraction coupling and contribute to muscle weakness in MG patients. Titin antibodies may serve as tumor markers in early-onset MG patients.

Microscopic polyangiitis and myasthenia gravis: the battle of Occam and Hickam

Microscopic polyangiitis (MPA) is a pauci-immune, necrotising, small-vessel vasculitis with an incidence of 3.6 per million population that typically presents in adulthood. Myasthenia gravis (MG), the most common disorder of the neuromuscular junction is rare, with an incidence of four per million population. We present the case of an adolescent girl previously diagnosed with MPA at age 7 years who presented with breathlessness and respiratory failure aged 15 years. The respiratory symptoms were due to thymoma-MG, which was successfully treated with cholinesterase inhibitors and thymectomy. This case report illustrates that the well-established doctrines of Occam's razor and of 'common conditions occurring commonly' are not universally applicable, and that in the adolescent age group, one should still consider Hickam's dictum.

[Antireceptor and antichannel autoantibodies]

This review of literature concerns the different autoantibodies directed against membrane receptors and ion channels. The target antigens, the associated pathologies, the pathogenesis and the methods of detection of these autoantibodies will be addressed. Some of these autoantibodies are thought to be closely related to the autoimmune disease whereas for some others their pathogenesis role is still unclear. Overall, the roles of antibodies are different between diseases, but the presence of such autoantibodies support the basis of intervening immunotherapy, antibody titers predicted the activity of the diseases and some of them are very specific and become the useful markers for the diagnosis. Some autoantibodies are detected routinely as the antiacetylcholine receptor, voltage-gated potassium and calcium channels autoantibodies whereas most of them are detected very rarely and only by specialized laboratories. This review will be divided in three parts with the following classification: the first group of autoantibodies directed against membrane receptors included receptors with an enzymatic activity (mostly tyrosine kinase) with one transmembrane domain, receptors associated to G protein with seven transmembrane domains, ion channels and receptors associated to the membrane by the glycosyl phosphatidyl inositol and the second group of intracellular receptor autoantibodies directed to the estrogens, androgens, lamin and kinesin receptors.

Myasthenia gravis: clinical, immunological, and therapeutic advances

We give an update on clinical, immunological, and therapeutic advances in the field of myasthenia gravis, including a summary of suggested therapeutic recommendations.

The significance of titin antibodies in myasthenia gravis--correlation with thymoma and severity of myasthenia gravis

Myasthenia gravis (MG) is caused by autoantibodies to acetylcholine receptors (AChR). Non-AChR muscle autoantibodies, such as titin antibodies, are present in sera of many MG patients. To study the correlation between titin antibodies and the features of MG, the cDNA segment encoding MGT-30 was amplified and sequenced. The cloned MGT-30 cDNA was expressed in vector pET-30a, and then transfected into E.coli. BL21. We examined titin antibodies in sera of 265 normal subjects, 154 MG patients with different thymic pathology and 48 patients with other neurological diseases. Titin antibodies occurred more frequently in MGT, especially in MG with epithelial predominant-thymoma, and were correlated with the severity of disease. The levels of titin antibodies were reduced 6 months after thymectomy. The specificity of titin antibodies for the detection of thymoma was higher than that of CT examination in MG with thymoma. These results suggest that titin antibodies could be useful in both diagnosis and follow-up of MG patients with thymoma.

Disease severity and outcome in thymoma myasthenia gravis: a long-term observation study

Thymomas occurring in myasthenia gravis (MG) are usually of the cortical subtype and are usually treated by thymectomy. However, the factors that influence MG outcome in thymoma MG patients are not known. In a long-term study, MG severity and treatment was observed in 24 thymoma and 24 non-thymoma MG patients for up to 30 years, and the occurrence of muscle autoantibodies was assayed. The rate of complete stable remission was low and did not differ between the two groups. There was no significant difference in MG severity between thymoma and non-thymoma MG patients at any time during the study. Titin and ryanodine receptor (RyR) antibody occurrence was significantly higher in thymoma MG patients. Four thymoma (all titin and RyR antibody positive) and two non-thymoma (both titin and one RyR antibody positive) MG patients died from MG-related respiratory insufficiency. Seventy percent of thymoma and 75% of non-thymoma MG patients were treated with immunosuppressive drugs. The number of patients who received plasmapheresis did not differ in those who were treated because of acute MG deterioration, irrespective of planned surgery.This study shows equal MG severity and outcome in thymoma and non-thymoma MG, but the presence of RyR antibodies in thymoma MG and titin/RyR in non-thymoma MG indicates a less favorable prognosis.

Autoantibodies to ion channels at the neuromuscular junction

Autoantibodies directed against voltage- or ligand-gated ion channels and their associated proteins at the neuromuscular junction give rise to a family of neurological autoimmune diseases. Antibodies to acetylcholine receptors or muscle-specific kinase present on the postsynaptic muscle membrane are associated with different forms of myasthenia gravis (MG). Antibodies to the presynaptic voltage-gated potassium and calcium channels are responsible for acquired neuromyotonia and Lambert-Eaton myasthenic syndrome (LEMS), respectively. The patients respond to immunotherapies and their plasma can transfer defects in neuromuscular transmission to mice, indicating that these are antibody-mediated conditions. In a small proportion of cases, ion channel antibodies have also been implicated in neurological dysfunction in the central nervous system. In these conditions, a proportion of the patients have an underlying tumour, thymoma in both MG and neuromyotonia and small cell lung carcinoma in LEMS, emphasising the putative role of autoimmunity to tumour antigens as a cause of neurological disease.